Paper calender roll



D60 13, 1955 Y DE WITT J. cHRlsTlE 3,291,039

PAPER GALENDER ROLL Filed April 20, 1964 INVENTOR. DEWITT J. CHRISTIE United States Patent O 3,291,039 PAPER CALENDER ROLL De Witt J. Christie, Slingerlauds, N.Y., assgnor to John A. Manning Paper Co., Inc., Troy, N.Y. Filed Apr. 20, 1964, Ser. No. 360,930 8 Claims. (Cl. 10D-162) This invention relates to an improved calendar of the type used to finish paper stock. More particularly, it relates to a supercalender incorporating a paper roll in which thermally upgraded paper is used..

Paper machines are commonly used with one or more pairs of closely spaced calender rolls which process the paper issuing from the machines. The rolls have hard smooth surfaces and the dry paper web is fed into the nip thereof, with resultant compression of paper and smoothing of its surface to impart a gloss thereto. The rolls are ordinarily made of carefully machined, highly polished iron or steel, which provides highly satisfactory finishing of most paper.

However, a pair of steel rolls wii-l generally not provide satisfactory operation when very fine Istock is to be calendered. The attainable tolerances in the concentrictiy of the rolls and the spacing `between them `are of the same order of magnitude as the thickness of the material being calendered and therefore, slight variations in spacing along the length -of the rolls result in a substantial difference in the pressure applied to various portions of the passing web. Much of the we-b therefore receives insufiicient pressure from the rolls for adequate smoothing of its surface. The same effect may result from slight variations in the thickness of the web itself.

Therefore, when thin paper is to be calendered a supercalender or paper calender is used. A paper calender has a plurality of vertically stacked. chilled iron rolls or similarly functioning rolls between which are composition or filled rolls. These composition rolls commonly have bodies formed by pressing together disks of fibrous material such as cotton, paper or the like. Specifically, the disks are stacked face-to-face on a core or shaft and two end plates at the ends of the stack are compressed, e.g. by nuts threaded on the ends of the shaft, to align the body and. apply a large compressive stress thereto. The compression effectively makes a monolithic structure out of the paper disks and this structure is relatively hard. Next, the composition roll thus formed is turned to provide a peripheral surface possessing the necessary nishing characteristics.

The composition roll is then placed in a calender stack adjacent to a metal roll or rolls. The metal rolls are often purposely heated to obtain certain results. In the calendering or finishing operation such direct heat and heat from friction or other causes heats the composition roll. That is, the ro-ll body takes on heat either by reason of a frictional action or because an adjacent roll is heated. The weight of the chilled iron rolls, usu-ally augmented by additional force through hydraulic loading or through weights and levers, causes an indentation in the nip between each iron roll-composition roll pair, resulting in a speed differential in the nip. The paper to be supercalendered is fed through such a nip so that the sliding, frictional polishing action caused. by the speed differential, produces a high gloss on the paper.

The resilience -of the composition roll produces a fairly equal pressure across the width of the paper web, thus eliminating the problem, noted above, involved in the use of a pair of steel rolls. It should be noted that the resilience spoken of is a matter of degree. The composition roll is hard and smooth to the touch, but it is substantially more resilient than iron or steel. In order to permit the removal of imperfections from the paper 3,2%,039 Patented Dec. 13, 1966 webs, which might damage the composition roll, paper calenders are generally not used. in line with paper machines.

A major problem associated with the use of paper calenders is the inability of composition rolls to Withstand the high temperatures in the nips between them and the associated chilled iron rolls, particularly with the shock impact of being repeatedly compressed by the iron rolls. Cotton and paper fibers on the roll body disintegrate in this environment, leading to a condition known as burning The burning of the roll body causes the surface thereof t-o become uneven, broken down and checked so that the roll is rendered unfit for further service. The composition roll must then be removed from the calender for remachining to remove these defects. Thus, there is an ever occurring need for refinishing, which is an expensive and time consuming operation.

Moreover, considerable expense results from the down time of the calender and the labor involved in replacing the burned rolls.

Previous efforts to improve the life of filled rolls have included water cooling the steel cores thereof; making the filling from asbestos, either alone or in conjunction with cellulose, and using so-called heat resistant fibers, e.g. ramie, in conjunction with cellulose. These expedients have helped but none have satisfactorily solved the problem.

It is a primary object of this invention to provide a calender incorporating a composition roll which will not readily deteriorate from the heat and compressive forces prevalent in the nip between the composition roll and a chilled iron roll cooperating therewith. More specifical- 1y, an object of the invention is to provide a composition roll which has a life span substantially greater than that of prior composition rolls incorporating cellulosic material such as paper or cotton.

Another object of the invention is to provide a paper calender incorporating a composition roll formed of compressed cellulosic disks of paper or cotton disks and characterized by a relatively long life under the usual conditions of use.

Other objects of the invention will in par-t be obvious and will in part appear hereinafter.

The invention accordingly comprises the features of construction, combination of elements, and arrangement ofV parts which will be exemplified in t-he construction hereinafter set forth, and the scope of the invention will be indicated in the claims.

For a fuller understanding of the nature and objects of the invention, reference should be had to the following detailed description taken in connection with the accompanying drawings, in which:

FIG. l is a schematic diagram of a calendar arranged for operation according lto the present invention, and

FIG. 2 is a perspective view of ra composition roll and associated iron 4roll used in the calender of FIG. l.

In general the present invention involves the use of specially treated cellulosic material in the roll body of composition calender rolls. T-he treatment relates to what is believed to be a chemical modification of the cellulosic material which materially improves its thermal stability. It is applicable to cellulosic materials in various forms, such as paper, cloth and nonwovens. Such treated material is designated herein as thermally upgraded.

Many thermally upgrading treatments have been specifically developed for the electrical industry, wherein cellulosic insulations thus treated and sealed in containers with oil, steel and copper have outlasted untreated cellulosic materials by a wide margin. These treatments also extend the life of a celluiose product in air. Among e.g. calcium carbonate.

the treatments known to improve the thermal stability of cellulose, i.e. provide thermally upgraded material, are acetylation and cyanoethylation, which entail chemical modification of the cellulose molecule. Urea .and melamine and various derivatives of these substances are also known 4to provide satisfactory results. A partial list of publica-tions of various thermally upgrading treatments includes the following U.S. patents:

T-hermally upgraded cellulosic material is characterized by reduction in brittleness and a reduction in the loss of strength, as compared with untreated material, after prolonged exposure to elevated temperatures.

A preferred thermally upgraded material is produced by incorporating into the cellulosic starting material a stabilizer which is a cationic condensation product of formaldehyde and one or more members of the group consisting of dicyandiamide, guanidine dicyanoguanidine and aliphatic amides. The amount of stabilizer used is from 0.5 |to percent of the dry weight of the starting material. A satisfactory stabilizer is a dicyandiamideformaldehyde condensate sold by Ciba Company, Inc. in the form of a 30% aqueous colloidal solution under the .tradmeark Lyox SBK. The stabilizer is added to the cellulosic material together with an acid acceptor such as the salt of an alkali earth metal and a weak acid,

In the case of paper, the stabilizer and acid acceptor may be added to the fiber slurry in the beater, during passage through the paper machine, or in an off-machine process by means of a water spray or the like. 'Ihe latter method of application is, of course, used if a nonwoven or woven cloth is to be thermally upgraded. Paper -treated in this manner -has been found to exhibit a marked increase in the retention of tensile strength and tear strength, as compared with untreated paper, after prolon-ged exposure to eleva-ted temperatures. It is also characterized by a material reduction in brittleness after such exposure.

Another preferred process for the production of thermally upgraded cellulosic material makes use of a cyclic substitu-ted urea. For example, a water-soluble substituted urea such as ethyl triazone or ethylene urea may be added to cellulosic fibers in the amount af about 0.5 to 10 percent of the dry weight of the cellulose. The resulting product again exhibits `the characteristics of thermally upgraded material.

FIG. 1 shows in schematic form a calender l10 incorporating calendar rolls embodying the present invention.

The calendar includes a stack of alternate composition or filled rolls 12 land chilled iron rolls 14. The rolls 12 and 14 are mounted in a frame (not shown) which includes bearings and drive elements for rotation of the rolls and also means for compressing the stack to provide the requisite pressure in the nips between the rolls. A paper web 15 on a feed roll 16 passes over a guide roll 18 and between the top composition roll 112 and the adjacent `roll 14, so as to be compressed in the nip -between these rolls. The paper then travels along a zigzag path through successive nips, with fly rolls 20 providing for reversal of direction and also maintaining the correct tension in the web. After leaving the bottom roll 12, the web 15 passes over a second guide roll 22 to a take-up roll 24.

FIG. 2 shows in greater detail the structure of one of the composition rolls 12 used in the calender of FIG. 1. The roll has an inner shaft or core 26 which extends through a stack of paper disks 28. The disks are compressed between a pair of end plates 30, which may be forced against the shaft by nuts 32 threaded onto the 4 shaft 26. The disks 28 are of thermally upgraded paper, and the stack has been machined after compression to form a smooth surface 34.

The utility of the invention is shown by the following examples, which are merely illustrative and do not limit the scope of the invention:

As a control, a composition roll was made of disks of rope paper having a thickness of 0.0025 inch. The hardness of the nished roll was 86 durometer. The paper in this roll, which is illustrative of the prior art, was not treated according to the present invention. The roll was installed in a calender between a pair of chilled iron rolls. The nip pressure was 2000 pounds per lineal inch and the calender was driven at a speed of feet per minute.

In accordance with the usual practice, the iron rolls were heated. A half hour after the beginning of the test, the temperatures monitored along the iron rolls were in the range of to 250 F. The monitored temperature along the intermediate composition roll varied from 190 to 210 F. Two hours after the beginning of the test, the temperatures measured at various points along the iron rolls were in the range of 260 to 300 F., and the temperatures along the composition roll varied from 240 to 290 F. The temperatures remained at approximately these levels for the remainder of the test. The composition roll failed in somewhat less than 15 hours continuous running time.

A second composition roll was made exactly the same as the roll used in Example I, except that the paper was thermally upgraded paper, treated in this case with the reaction product of dicyandiamide formaldehyde in the manner described above. The finished roll had a hardness of 87 durometer. Initially heat was applied to the chilled iron rolls at a greater rate than in Example I and therefore, these rolls and the composition roll came up to final temperature in a somewhat shorter time. The nip pressure and calender speed were the same as in Example I. The compsition roll failed after a 26-hour continuous run.

III

This test and the one following involved rag paper made from cotton rags and having a thickness of about 0.004 inch. As a control, a composition roll was made of untreated paper from this run. This roll had a hardness of about 86 durometer and was operated under substantially the same conditions as in Example I. It failed after a running time of about 19 hours.

Part of the paper run referred to in Example III was treated with ethylene urea. The weight of the ethylene urea added to the paper was about 2.5% of the weight of paper before treatment. A composition roll made of this paper had a hardness of about 86 durometer. It was run under essentially the same conditions as in Example III. The test was stopped after 51 hours although the roll had not yet failed.

The very substantial increase in composition roll life resulting from the present invention provides material decrease in the cost of supercalendering paper. This is, of course, due in part to the fact that fewer composition rolls are required for the processing of a given amount of paper. Also to be considered is the reduction in labor involved in replacing composition rolls in supercalenders, as well as the reduction in down time of the'supercalendering equipment.

As pointed out above, the lengthening of composition roll life results from the treatment of the cellulosic roll body with any of a number of additives which are known to provide thermal upgrading of cellulose. The thermal upgrading retards deterioration of the cellulose at elevated temperatures, with specific reference to its strength and brittleness, and it is believed that this particular aspect of thermal upgrading is of great importance in composition calender rolls. This follows from the immense pressure applied to the -composition rolls in the nips and also to the working of the paper as it undergoes temporary indentation therein.

Most of the chemicals known to provide thermal upgrading of cellulose are in the urea group, i.e. urea, its derivatives and similar substances. However, the invention is not limited to the use of these particular compounds.

It will thus be seen that the objects set forth above, among those made apparent from the preceding description, are eiciently attained and, since certain changes may be made in the above construction Without departing from the scope of the invention, it is intended that all matter contained in the above description or shown in the accompanying drawing shall be interpreted as illustrative and not in `a limiting sense.

It is also to be understood that the following claims are intended to cover all of the generic and specific features of the invention herein described, and all statements of the scope of the invention which, as a matter of language, might be said to fall therebetween.

I claim:

1. A composition roll for use in a calender that subjects the roll to elevated temperatures, said roll comprising (A) a core for rotatably mounting said roll, and

(B) a plurality of sheets of cellulosic bers (l) chemically treated with an additive selected from the group of compositions that render such fibers resistant to increased brittleness and to loss of strength due to exposure to elevated temperatures, and

(2) forming a multi-layer cylindrical composition body covering said core.

2. A composition roll according to claim 1 in which said sheets are annular disks compressed in an axial stack to form said cylindrical body.

3. A composition roll according to claim 1 in which said composition body has a cylindrical outer surface that consists substantially exclusively of said chemically treated cellulosic fibers.

4. A composition roll according to claim 1 in which said sheets are paper.

5. A composition roll according to claim 1 in which said additive is selected from the group consisting of urea compositions and urea derivative compositions.

6. A calender for the nishing of paper and like products, said calender (A) comprising a plurality of rolls, each of which is adjacent and in engagement with at least one other roll,

(B) at least one of said rolls having a composition body,

(C) said composition body comprising a plurality of pressed-together disks of cellulosic fibers that are chemically treated with an additive selected from the group of compositions that render such fibers resistant to increased brittleness and to loss of strength due to exposure to elevated temperatures.

7. A calender according to claim 6 in which said composition body has a cylindrical outer surface that consists substantially exclusively of said chemically treatedr cellulosic bers.

8. A calender according to claim 6 in which said sheets are paper and in which said additive is selected from the group consisting of urea compositions and urea derivative compositions.

References Cited by the Examiner UNITED STATES PATENTS 843,700 2/1907 Rusden 29-132 1,785,265 12/1930 Lade 29-132 X 1,854,509 4/1932 Fish 29-132 X 2,406,718 8/ 1946 Thomas.

2,987,802 6/1961 Quinn 29-132 X 2,991,326 7/1961 Ford et al. 174-17 FOREIGN PATENTS 2,758 41904 Great Britain.

LOUIS O. MAASSEL, Primary Examiner. 

1. A COMPOSITION ROLL FOR USE IN A CALENDER THAT SUBJECTS THE ROLL TO ELEVATED TEMPERATURES, SAID ROLL COMPRISING (A) A CORE FOR ROTATABLY MOUNTING SAID ROLL, AND (B) A PLURALITY OF SHEETS OF CELLULOSIC FIBERS (1) CHEMICALLY TREATED WITH AN ADDITIVE SELECTED FROM THE GROUP OF COMPOSITIONS THAT RENDER SUCH FIBERS RESISTANT TO INCREASED BRITTLENESS AND TO LOSS THE STRENGTH DUE TO EXPOSURE TO ELEVATED TEMPERATURES, AND (2) FORMING A MULTI-LAYER CYLINDRICAL COMPOSITION BODY COVERING SAID CORE. 